AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    Students should be able to describe, with examples, the relationship…

    Full specification wording

    Energy transfers in everyday appliances: Students should be able to describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use.

    The power rating printed on an appliance is the energy it transfers each second, in joules per second.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 6 of 6
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    The power rating printed on an appliance is the energy it transfers each second, in joules per second. An LED lamp near 10 W, a television near 100 W, a kettle near 2 000 W and an electric shower near 9 000 W are the numbers worth carrying into the exam. A larger rating means the stored energy changes faster: a 2 000 W kettle raises the thermal store of the water two hundred times faster than a 10 W lamp lights a room. To compare appliances properly you must combine the rating with the running time using E = P t, because a low power device left on all day can change stores by more than a high power device used for two minutes. Heating appliances carry the highest ratings, because raising temperature needs a great deal of energy.

    What earns the marks

    • The power rating stated as the energy transferred each second.
    • A sensible power rating quoted for a named appliance.
    • Naming the store that changes, such as the thermal store of the water in a kettle.
    • Combining the rating with a running time using E = P t to compare two appliances.

    Common mistakes and how to put them right

    • Describing a power rating as the total energy an appliance uses.

    • Quoting a kettle as 2 W or an LED lamp as 2 000 W because the magnitudes have not been learned.

    • Comparing appliances by power rating alone when their running times differ.

    • Saying the energy of the appliance increases rather than naming the store that changes.

    Exam tips

    • Learn one plausible rating for a lamp, a television, a kettle and a shower so you can always quote an example.
    • 'With examples' in a question means at least one named appliance with a number attached.
    • Say which store changes and in which direction, because 'energy increases' alone is not enough.

    Try the lesson

    The start of the Energy transfers in everyday appliances: Students should be able to describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use. lesson, made from checked teaching notes for this specification point.

    Have a go first

    A 2000 W kettle and a 700 W microwave are each switched on for the same length of time. Which appliance transfers more energy from the mains electricity supply in that time?

    Listen

    The power rating printed on an appliance is the energy it transfers each second, in joules per second. An LED lamp near 10 W, a television near 100 W, a kettle near 2 000 W and an electric shower near 9 000 W are the numbers worth carrying into the exam. A larger rating means the stored energy changes faster: a 2 000 W kettle raises the thermal store of the water two hundred times faster than a 10 W lamp lights a room. To compare appliances properly you must combine the rating with the running time using E = P t, because a low power device left on all day can change stores by more than a high power device used for two minutes. Heating appliances carry the highest ratings, because raising temperature needs a great deal of energy. A strong answer earns marks for these points. the power rating stated as the energy transferred each second. a sensible power rating quoted for a named appliance. naming the store that changes, such as the thermal store of the water in a kettle. combining the rating with a running time using E = P t to compare two appliances. Exam tip: Learn one plausible rating for a lamp, a television, a kettle and a shower so you can always quote an example.

    See it

    A top-down flowchart. The top node reads 'Power rating = energy transferred each second' and branches to four appliance nodes: 'LED lamp near 10 W', 'Television near 100 W', 'Kettle near 2 000 W' and 'Electric shower near 9 000 W'. The kettle node also leads to a node reading 'Thermal store of the water changes'. All four appliance nodes lead to a node reading 'Larger rating means stored energy changes faster', which leads to 'Combine rating with running time using E = P t', which finally leads to 'Low power device left on all day can change stores more than a high power device used for two minutes'.
    It shows that the power rating is the energy transferred each second, gives example ratings for four appliances, and shows that rating must be combined with running time using E = P t to compare appliances.

    Key words

    Say what each word means before you turn the card.

    power rating

    Try answering aloud or in your head before turning the card.

    typical appliance powers

    Try answering aloud or in your head before turning the card.

    running time

    Try answering aloud or in your head before turning the card.

    See every definition
    power rating
    The energy an appliance transfers each second, in joules per second, as printed on the appliance.
    typical appliance powers
    Plausible ratings worth learning for a lamp, a television, a kettle and a shower, so an example can always be quoted.
    running time
    The time an appliance is used for, which must be combined with the rating using E = P t to compare appliances properly.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The top node reads 'Power rating = energy transferred each second' and branches to four appliance nodes: 'LED lamp near 10 W', 'Television near 100 W', 'Kettle near 2 000 W' and 'Electric shower near 9 000 W'. The kettle node also leads to a node reading 'Thermal store of the water changes'. All four appliance nodes lead to a node reading 'Larger rating means stored energy changes faster', which leads to 'Combine rating with running time using E = P t', which finally leads to 'Low power device left on all day can change stores more than a high power device used for two minutes'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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